Using little more than a few perforated sheets of plastic and a staggering amount of number crunching, Duke engineers have demonstrated a three-dimensional acoustic cloak. The new device reroutes sound waves to create the impression that both the cloak and anything beneath it are not there.
The acoustic cloaking device works in all three dimensions, no matter which direction the sound is coming from or where the observer is located, and holds potential for future applications such as sonar avoidance and architectural acoustics.
The materials manipulating the behavior of sound waves are simply plastic and air. Once constructed, the device looks like several plastic plates with a repeating pattern of holes poked through them. The plates are stacked on top of one another to form a sort of pyramid.
The cloak must alter the waves’ trajectory to match what they would look like had they had reflected off a flat surface. Because the sound is not reaching the surface beneath, it is traveling a shorter distance and its speed must be slowed to compensate.
To test the cloaking device, researchers covered a small sphere with the cloak and “pinged” it with short bursts of sound from various angles. Using a microphone, they mapped how the waves responded and produced videos of them traveling through the air.
Learn about an Acoustic Liner for Turbomachinery Applications.